All those categories are up, says Brewer, and she said nitro cold brew is "really resonating with our male millennials." A reason could be that Starbucks is marketing the nitrogen-infused coffee much like craft brewers do beer, with baristas handing out samples and pulling it from a draft spigot.

But sales of the other cold drinks are "not enough yet" to offset the decline in Frappuccino sales during the first three quarters of its fiscal 2018, compared with last year, Brewer said.